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Nitrogen fertilization is critical to optimize short-term crop yield, but its long-term effect on soil organic C (SOC) is uncertain. Here, we clarify the impact of N fertilization on SOC in typical maize-based (Zea mays L.) Midwest U.S. cropping systems by accounting for site-to-site variability in maize yield response to N fertilization. Within continuous maize and maize-soybean [Glycine max (L.) Merr.] systems at four Iowa locations, we evaluated changes in surface SOC over 14 to 16 years across a range of N fertilizer rates empirically determined to be insufficient, optimum, or excessive for maximum maize yield. Soil organic C balances were negative where no N was applied but neutral (maize-soybean) or positive (continuous maize) at the agronomic optimum N rate (AONR). For continuous maize, the rate of SOC storage increased with increasing N rate, reaching a maximum at the AONR and decreasing above the AONR. Greater SOC storage in the optimally fertilized continuous maize system than in the optimally fertilized maize-soybean system was attributed to greater crop residue production and greater SOC storage efficiency in the continuous maize system. Mean annual crop residue production at the AONR was 22% greater in the continuous maize system than in the maize-soybean system and the rate of SOC storage per unit residue C input was 58% greater in the monocrop system. Our results demonstrate that agronomic optimum N fertilization is critical to maintain or increase SOC of Midwest U.S. cropland.

Fertilizing maize at an optimum nitrogen rate is imperative to maximize productivity and sustainability. Using a combination of long-term ( n  = 379) and short-term ( n  = 176) experiments, we show that the economic optimum nitrogen rate for US maize production has increased by 2.7 kg N ha −1 yr −1 from 1991 to 2021 (1.2% per year) simultaneously with grain yields and nitrogen losses. By accounting for societal cost estimates for nitrogen losses, we estimate an environmental optimum rate, which has also increased over time but at a lower rate than the economic optimum nitrogen rate. Furthermore, we provide evidence that reducing rates from the economic to environmental optimum nitrogen rate could reduce US maize productivity by 6% while slightly reducing nitrogen losses. We call for enhanced assessments and predictability of the economic and environmental optimum nitrogen rate to meet rising maize production while avoiding unnecessary nitrogen losses. Maize production is dependent on Nitrogen fertilizer input. Here, the authors use long-term and short-term experiments to demonstrate that economic and environmental optimum nitrogen fertilization rates have increased between 1991 and 2021.

Inclusion of perennial vegetation filter strips (PFSs) in the toeslope of annual cropland watersheds can decrease NO3−–N losses to ground and surface waters. Although PFSs are similar to riparian buffers, the processes responsible for NO3−–N removal from PFSs are not well understood. Our objectives were to (i) determine the importance of denitrification as a sink for NO3−–N loss from PFSs and (ii) evaluate how PFSs alter the biophysical processes that affect the relative importance of N2O and N2 emissions. To address our objectives, we used a coupled field laboratory approach with experimental watersheds that included the following treatments: (i) PFSs covering the bottom 10% of the watershed and an annual corn–soybean crop rotation covering the remaining upslope 90% (PFS); (ii) 100% corn–soybean rotation (CORN); and (iii) 19‐yr‐old 100% restored native grassland (RNG). In situ N2O flux rates and laboratory N2O/(N2 + N2O) ratios were highest in CORN watersheds followed by PFS and RNG watersheds. In contrast, potentially mineralizable C and denitrification enzyme activity (DEA) were highest in PFS and RNG watersheds and lowest in CORN watersheds. Furthermore, there was a negative correlation between N2O/(N2 + N2O) ratio and DEA. In the laboratory, N2 fluxes were highest in PFS followed by RNG and CORN. These results indicate that PFS watersheds support greater total denitrification while emitting less N2O than croplands. Greater potentially mineralizable C in PFS and RNG suggest C availability is an important factor affecting more complete denitrification. These results suggest PFSs function similar to riparian buffers and have potential to reduce NO3−–N losses from annual croplands by denitrification to N2.

Cover crops (CCs) can reduce nitrogen (N) loss to subsurface drainage and can be reimagined as bioenergy crops for renewable natural gas production and carbon (C) benefits (fossil fuel substitution and C storage). Little information is available on the large-scale adoption of winter rye for these purposes. To investigate the impacts in the North Central US, we used the Root Zone Water Quality Model to simulate corn-soybean rotations with and without winter rye across 40 sites. The simulations were interpolated across a five-state area (IA, IL, IN, MN, and OH) with counties in the Mississippi River basin, which consists of ∼8 million ha with potential for rye CCs on artificially drained corn-soybean fields (more than 63 million ha total). Harvesting fertilized rye CCs before soybean planting in this area can reduce N loads to the Gulf of Mexico by 27% relative to no CCs, and provide 18 million Mg yr −1 of biomass-equivalent to 0.21 EJ yr −1 of biogas energy content or 3.5 times the 2022 US cellulosic biofuel production. Capturing the CO 2 in biogas from digesting rye in the region and sequestering it in underground geologic reservoirs could mitigate 7.5 million Mg CO 2 yr −1 . Nine clusters of counties (hotspots) were identified as an example of implementing rye as an energy CC on an industrial scale where 400 Gg yr −1 of rye could be sourced within a 121 km radius. Hotspots consisted of roughly 20% of the region’s area and could provide ∼50% of both the N loss reduction and rye biomass. These results suggest that large-scale energy CC adoption would substantially contribute to the goals of reducing N loads to the Gulf of Mexico, increasing bioenergy production, and providing C benefits.

Loss of biodiversity and degradation of ecosystem services from agricultural lands remain important challenges in the United States despite decades of spending on natural resource management. To date, conservation investment has emphasized engineering practices or vegetative strategies centered on monocultural plantings of nonnative plants, largely excluding native species from cropland. In a catchment-scale experiment, we quantified the multiple effects of integrating strips of native prairie species amid corn and soybean crops, with prairie strips arranged to arrest run-off on slopes. Replacing 10% of cropland with prairie strips increased biodiversity and ecosystem services with minimal impacts on crop production. Compared with catchments containing only crops, integrating prairie strips into cropland led to greater catchment-level insect taxa richness (2.6-fold), pollinator abundance (3.5-fold), native bird species richness (2.1-fold), and abundance of bird species of greatest conservation need (2.1-fold). Use of prairie strips also reduced total water runoff from catchments by 37%, resulting in retention of 20 times more soil and 4.3 times more phosphorus. Corn and soybean yields for catchments with prairie strips decreased only by the amount of the area taken out of crop production. Social survey results indicated demand among both farming and nonfarming populations for the environmental outcomes produced by prairie strips. If federal and state policies were aligned to promote prairie strips, the practice would be applicable to 3.9 million ha of cropland in Iowa alone.

The effect of climate change on crop production and nitrate-nitrogen (NO 3 -N) pollution from subsurface drained fields is of a great concern. Using the calibrated and validated RZWQM2 (coupled with CERES-Maize and CROPGRO in DSSAT), the potential effects of climate change and elevated atmospheric CO 2 concentrations (CO 2 ) on tile drainage volume, NO 3 -N losses, and crop production were assessed integrally for the first time for a corn-soybean rotation cropping system near Gilmore City, Iowa. RZWQM2 simulated results under 20-year observed historical weather data (1990–2009) and ambient CO 2 were compared to those under 20-year projected future meteorological data (2045–2064) and elevated CO 2 , with all management practices unchanged. The results showed that, under the future climate, tile drainage, NO 3 -N loss and flow-weighted average NO 3 -N concentration (FWANC) increased by 4.2 cm year −1 (+14.5 %), 11.6 kg N ha −1  year −1 (+33.7 %) and 2.0 mg L −1 (+16.4 %), respectively. Yields increased by 875 kg ha −1 (+28.0 %) for soybean [ Glycine max (L.) Merr.] but decreased by 1380 kg ha −1 (−14.7 %) for corn ( Zea mays L.). The yield of the C 3 soybean increased mostly due to CO 2 enrichment but increased temperature had negligible effect. However, the yield of C 4 corn decreased largely because of fewer days to physiological maturity due to increased temperature and limited benefit of elevated CO 2 to corn yield under subhumid climate. Relative humidity, short wave radiation and wind speed had small or negligible impacts on FWANC or grain yields. With the predicted trend, this study suggests that to mitigate NO 3 -N pollution from subsurface drained corn-soybean field in Iowa is a more challenging task in the future without changing current management practices. This study also demonstrates the advantage of an agricultural system model in assessing climate change impacts on water quality and crop production. Further investigation on management practice adaptation is needed.

Twelve small watersheds in central Iowa were used to evaluate the effectiveness of prairie filter strips (PFS) in trapping sediment from agricultural runoff . Four treatments with PFS of different size and location (100% rowcrop, 10% PFS of total watershed area at footslope, 10% PFS at footslope and in contour strips, 20% PFS at footslope and in contour strips) arranged in a balanced incomplete block design were seeded in July 2007. All watersheds were in bromegrass (Bromus L.) for at least 10 yr before treatment establishment. Cropped areas were managed under a no-till, 2-yr corn (Zea mays L.)–soybean [Glycine max. (L.) Merr.] rotation beginning in 2007. About 38 to 85% of the total sediment export from cropland occurred during the early growth stage of rowcrop due to wet field conditions and poor ground cover. The greatest sediment load was observed in 2008 due to the initial soil disturbance and gradually decreased thereafter. The mean annual sediment yield through 2010 was 0.36 and 8.30 Mg ha−1 for the watersheds with and without PFS, respectively, a 96% sediment trapping efficiency for the 4-yr study period. The amount and distribution of PFS had no significant impact on runoff and sediment yield, probably due to the relatively large width (37–78 m) of footslope PFS. The findings suggest that incorporation of PFS at the footslope position of annual rowcrop systems provides an effective approach to reducing sediment loss in runoff from agricultural watersheds under a no-till system.

While subsurface drip irrigation supplies water to meet crop needs with high water use efficiency, it might cause low O(2) levels around crop roots and affect plant growth and yield. A modified flow apparatus was used in the laboratory to investigate the impact of aeration following subsurface drip irrigation on transient air permeability. Disturbed samples from two soils from China, a Brown Forest soil (sandy loam) and Lou soil (silty clay loam), were repacked to construct soil columns with various bulk densities (1.3, 1.35, 1.4, 1.45, 1.5, and 1.55 g cm(-3)). Subsurface drip irrigation (350 mL) was performed at the 17-cm soil depth. Aeration (1050 mL) was conducted through the emitter of the subsurface drip irrigation system for 5 min. The results showed that air permeability was affected by soil texture and bulk density. The measured air permeability from the modified apparatus was comparable to that from the classical apparatus. Soil air permeability after irrigation was reduced by 88.2, 70.1, and 42.5% for the Brown Forest soil with a bulk density of 1.3, 1.4, and 1.5 g cm(-3), respectively, and 71.2, 65.4, and 54.3%, respectively, for the Lou soil. A short-period aeration following irrigation quickly improved soil air permeability, however. The air permeability level within 10 min after aeration was 3.7, 2.0, and 1.5 times that before aeration for the Brown Forest soil with a bulk density of 1.3, 1.4, and 1.5 g cm(-3), respectively, and 3.0, 2.5 and 2.0 times, respectively, for the Lou soil. It seems a feasible and economical approach to improve soil air permeability by aerating the soil through a subsurface irrigation system following irrigation.

Agriculture in the US Corn Belt is under increasing pressure to produce greater quantities of food, feed and fuel, while better protecting environmental quality. Key environmental problems in this region include water contamination by nutrients and herbicides emitted from cropland, a lack of non-agricultural habitat to support diverse communities of native plants and animals, and a high level of dependence on petrochemical energy in the dominant cropping systems. In addition, projected changes in climate for this region, which include increases in the proportion of precipitation coming from extreme events could make soil and water conservation in existing cropping systems more difficult. To address these challenges we have conducted three cropping systems projects in central Iowa: the Marsden Farm Cropping Systems experiment, the Science-based Trials of Row-crops Integrated with Prairies (STRIPs) experiment, and the Comparison of Biofuel Systems (COBS) experiment. Results from these experiments indicate that (1) diversification of the dominant corn–soybean rotation with small grains and forage legumes can permit substantial reductions in agrichemical and fossil hydrocarbon use without compromising yields or profitability; (2) conversion of small amounts of cropland to prairie buffer strips can provide disproportionately large improvements in soil and water conservation, nutrient retention, and densities of native plants and birds; and (3) native perennial species can generate large amounts of biofuel feedstocks and offer environmental benefits relative to corn- and soybean-based systems, including greater carbon inputs to soil and large reductions in nitrogen emissions to drainage water. Increasing biodiversity through the strategic integration of perennial plant species can be a viable strategy for reducing reliance on purchased inputs and for increasing agroecosystem health and resilience in the US Corn Belt.

Nitrate‐nitrogen (NO3–N) loading to surface water bodies from subsurface drainage is an environmental concern in the midwestern United States. The objective of this study was to investigate the effect of various land covers on NO3–N loss through subsurface drainage. Land‐cover treatments included (i) conventional corn (Zea mays L.) (C) and soybean [Glycine max (L.) Merr.] (S); (ii) winter rye (Secale cereale L.) cover crop before corn (rC) and before soybean (rS); (iii) kura clover (Trifolium ambiguum M. Bieb.) as a living mulch for corn (kC); and (iv) perennial forage of orchardgrass (Dactylis glomerata L.) mixed with clovers (PF). In spring, total N uptake by aboveground biomass of rye in rC, rye in rS, kura clover in kC, and grasses in PF were 14.2, 31.8, 87.0, and 46.3 kg N ha−1, respectively. Effect of land covers on subsurface drainage was not significant. The NO3–N loss was significantly lower for kC and PF than C and S treatments (p < 0.05); rye cover crop did not reduce NO3–N loss, but NO3–N concentration was significantly reduced in rC during March to June and in rS during July to November (p < 0.05). Moreover, the increase of soil NO3–N from early to late spring in rS was significantly lower than the S treatment (p < 0.05). This study suggests that kC and PF are effective in reducing NO3–N loss, but these systems could lead to concerns relative to grain yield loss and change in farming practices. Management strategies for kC need further study to achieve reasonable corn yield. The effectiveness of rye cover crop on NO3–N loss reduction needs further investigation under conditions of different N rates, wider weather patterns, and fall tillage.